The broad objective of this project is to understand both the biochemical mechanism and biological function of DNA helicases. One of the helicases that is a focus of this proposal is distinctive in that it recognizes a specific single-stranded DN sequence while translocating and, in response to that interaction, alters its biochemical behavior in unprecedented ways. The other helicases comprise a broad family of related orthologs and paralogs, the RecQ-family. The RecQ helicases interact specifically with numerous accessory proteins that take advantage of their unique unwinding capacities and that also alter their DNA unwinding capabilities. Finally, a third group of helicases constitutes a heterogeneous collection of helicases that share the common capacity to remodel protein-ssDNA complexes. Understanding the mechanism and function of such motor proteins are goals of this research proposal. In the past decade, it has become possible to reliably examine helicases and DNA motor proteins at the single-molecule level. This capability has transformed mechanistic analysis of this important family of proteins. Single-molecules of these helicases will be imaged to literally visualize the manner by which they bind and release their partner proteins in order to better understand their functions in important biological regulatory processes. We will use both single-molecule and ensemble methods to understand both mechanism and function.